An engine of a vehicle may be stopped and started during a vehicle drive cycle to conserve fuel. The engine may be stopped when the vehicle is stopped when driver demand torque is low. The engine may also be stopped while the vehicle is moving during low driver demand torque conditions while an electric machine provides torque to propel the vehicle. The stopped engine may be restarted if driver demand torque increases or if a battery is to be charged. However, for vehicles that are not propelled via an electric motor and that include an automatic transmission, it may be difficult to stop the engine in response to low driver demand torques because stopping the engine stops operation of a mechanically driven pump in the transmission that supplies pressurized fluid to activate transmission gears. Thus, the transmission may not operate as desired if the engine is stopped. Therefore, it may be desirable to provide a way to stop an engine and maintain transmission operation during low driver demand conditions so that engine fuel consumption may be reduced during low driver demand torque conditions and while the vehicle is stopped.
The inventors herein have recognized the above-mentioned issues and have developed a method for operating a vehicle driveline, comprising: activating an electric transmission pump in response to a request to stop an engine; and adjusting a speed of the electric transmission pump in response to a pressure in an accumulator.
By adjusting a speed of the electric transmission pump in response to a pressure in the accumulator, it may be possible to provide the technical result of reducing energy consumption of a vehicle while shifting a transmission of the vehicle. In particular, the transmission may be shifted while the engine is stopped so that if a driver requests engine torque, the transmission may be engaged in an appropriate gear for the present vehicle speed in a short period of time. In this way, the vehicle may respond quickly to a driver request even when an engine is stopped to improve vehicle drivability. Further, transmission electric pump speed may be adjusted responsive to an estimate of time between gear shifts so that a desired pressure may be available to stroke a gear clutch in time for a next gear shift.
The present description may provide several advantages. For example, the approach may reduce vehicle fuel consumption and improve response to a driver requesting driveline torque when an engine in the driveline is stopped rotating. Further, the approach may provide for partially engaging a plurality of gear clutches when an engine coupled to a transmission is stopped so that the transmission may be engaged in an appropriate gear for applying engine torque to vehicle wheels even as vehicle speed changes while the engine is stopped. Further still, the approach may reduce electrical power consumption by adjusting a speed of the electrical transmission pump to a speed that meets but does not significantly exceed a speed to timely stroke one or more transmission clutches during gear shifting. Additionally, the approach may provide desired shifting even when the transmission electric pump lacks flow capacity to close a transmission clutch in a desired amount of time.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.